In a digital wireless communication system, due to the multipath propagation environment, delayed waves cause mutual interference between symbols to produce distortion in the waveform of the signal, which can deteriorate the communication quality. Maximum likelihood sequence estimation is known as a technique for correcting such waveform distortion and improving the communication quality. Maximum likelihood sequence estimation is a technique of estimating a correct transmission symbol sequence by comparing a plurality of replica reception signals generated from transmission path impulse responses and a plurality of candidates for the transmission symbol sequence and reception sample signals sampled at symbol intervals from the actual reception signal. The comparison between a replica reception signal and a reception sample signal is performed using the square value of the difference between the replica reception signal and the reception sample signal, and this value is called a branch metric.
Patent Literature 1 discloses a technique for realizing good communication quality even in a propagation environment in which the delay time of a delayed wave is not an integral multiple of the symbol interval. Specifically, the technique of Patent Literature 1 includes performing maximum likelihood sequence estimation by using reception sample signals sampled from a reception signal at sample intervals shorter than the symbol intervals. In this technique, reception sample signals are sampled from a reception signal at sample intervals of 1/N of the symbol intervals and divided into N strings of reception sample signals, each including reception sample signals at symbol intervals. Then, maximum likelihood sequence estimation is performed using the branch metrics generated for each string.